Polypropylene compositions having improved impact strength containing polyethylene and ethylene-propylene copolymer



United States Patent 3,256,367 POLYPROPYLENE COMPOSITIONS HAVING IM- PROVE!) IMPACT STRENGTH CONTAINING POLYETHYLENE AND ETHYLENE-PROPYLENE COPOLYMER William M. Jayne, .lrx, Basking Ridge, N.J., assignor to gnipn Carbide Corporation, a corporation of New orr No Drawing. Filed Aug. 14, 1962, Ser. No. 216,727 5 Claims. (Cl. 260897) The invention relates to novel polypropylene compositions. More particularly, the invention relates to novel compositions comprising polypropylene, polyethylene, and ethylene/propylene copolymers o-r polyisobutylene which exhibit surprisingly improved impact strength.

Solid polypropylene is recognized in the plastics industry as possessing great commerical potential because it is superior in several respects to polyethylene. For example, polypropylene has a higher melting point, lower density, and greater stiffness modulus than does polyethylene. Polypropylene can also be produced in either amorphous or crystalline form by variation of the polymerization catalyst.

Polypropylene has been used for the manufacture of shaped articles, but some of its inherent deficiencies have, unfortunately, limited its use in many other applications for which it would otherwise be well suited. For example, its low impact strength, i.e., high shock sensitivity at temperatures below room temperature, is a disadvantage which has precluded its use for fibers, films, and other extruded and molded items, and, in particular, for containers and packaging materials.

In order to remedy the low impact resistance possessed by polypropylene, rubber products, such as polyisobutylene, have been added. While addition of rubbers has resulted in polypropylene compositions having improved impact resistance, the improvement has been achieved at the expense of obtaining a more opaque product having less stiffness, i.e., a lower secant modulus, and lower heat and air stability than unmodified polypropylene.

Thus there exists in the art a need for polypropylene having, particularly, higher impact strength than is available with presently known polypropylene-rubber compositions.

It has now been surprisingly discovered that poly-.

propylene compositions having higher impact strengths and stiffness and heat resistance properties comparable to any polypropylene or rubber-modified polypropylene heretofore available are obtained by the incorporation of a polyethylene having a density above about 0.91 into polypropylene-rubber compositions comprising a polypropylene having a density above about 0.89 and amorphou ethylene/propylene copolymer or polyisobutylene rubber.

It is an unusual phenomenon in the present invention that the improvement in polypropylene impact strength is realized only when the polyethylene is incorporated into polypropylene compositions containing either an amorphous ethylene-propylene copolymer rubber or polyisobutylene rubber. When other rubbers conventionally employed as additives in polypropylene, for example, polybutadiene and polyisoprene, are blended with polypropylene with or without polyethylene, the compositions do not exhibit the surprising great impact strength improvement found with the compositions of the present invention.

The polypropylene compositions of the invention generally comprise from about 50 percent by weight to about 96 percent by weight polypropylene, from about 2 per- Patented June 14, 1966 cent by weight to about 25 percent by weight polyethylene, and from about 2 percent by weight to about 25 perent by weight amorphous ethylene/propylene copolymer or polyisobutylene. Preferred polypropylene compositions comprise from about 65 to about 92 percent by weight polypropylene, from about 4 percent by weight to about 20 percent by weight polyethylene, and from about 4 percent by weight to about 15 percent by weight amorphous ethylene/propylene copolymer or polyisobutylene. The combined amount of polyethylene and amorphous ethylene/propylene copolymer or polyisobutylene in any polypropylene composition is preferably less than 35 percent by weight because of the desirable fiexural characteristics of such mixtures.

The polypropylenes useful in the compositions of this invention are normally solid polymers of propylene having' a melt flow at 44 p.s.i. and 230 C. below about 12 g./ 10 min. and preferably from about 2.0 to about 0.01 g./l0 min. While the density of the polypropylene used is not particularly critical, polypropylenes having a density above about 0.89 g./cc. are generally preferred. The polypropylene can be either amorphous or crystalline or partially crystalline.

Polyethylenes found to impart unexpected improvement in impact strength to polypropylene-rubber compositions are those normally solid polymers having a density of from about 0.91 to about 0.97 and higher and a melt index at 190 C. and 44 p.s.i. below about 100 dg./min. and particularly from about 1.0 to about 8.0 dg./rnin. The preferred density is about 0.96.

It has been found that only two rubbers, namely amorphous ethylene/propylene copolymers and polyisobutylene, can be used in admixture with polypropylene and polyethylene to secure the improvements and advantages of the compositions of this invention. Of these two, amorphous ethylene/propylene copolymers are preferred because greater impact strengths are obtained with lesser sacrifice of stiffness and oxygen and thermal stability. Amorphou ethylene/propylene copolymers are useful over a wide range of combined ethylene to combined propylene ratios, e.g., from about 25 percent by weight to about 95 percent by weight combined ethylene and from about 5 percent by weight to about percent by weight combined propylene. The preferred amorphous ethylene/ propylene copolymers comprise from about 35 percent by weight to about percent by weight combined ethylene and from about 20 percent by weight to about 65 percent by weight combined propylene. The ethylene/ propylene copolymers employed herein are normally solid copolymers having a melt index at 190 C. and 44 p.s.i. of less than about 1000 dg./min. and preferably less than about dg./ min.

By the term amorphous ethylene/propylene copolymers is meant those ethylene/propylene copolymers which are less than about 20 percent crystalline. The preferred ethylene/propylene copolymers are completely noncrystalline.

The polyisobutylenes employed herein have a melt index at C. and 44 p.s.i. of less than about 1 000 dg./min. and preferably less than about 100 dg./ min.

The three components of the composition herein described can be mixed together in any order using conventional hot processing equipment well known to the plastics art. For example, batch type equipment such as a Banbury mixer or a two-roll mill can be employed, or a finely ground mixture can be compounded in a screw extruder.

Masterbatch techniques are conveniently employed in preparing the mixtures. For example, if it is desired to prepare a polypropylene composition containing 10 percent by weight ethylene/propylene copolymer and 10 33 percent by weight polyethylene, a masterbatch of ethylene/ propylene copolymer and polyethylene is first prepared which contains equal weight amounts of these components. Subsequent 'letdown of the masterbatch at 4 250 C., and to produce strand cut pellets suitable for molding. The extruded strands were passed through a 40 C. cooling water bath, dried, and cut into approximately x A pellets. The mixture had the followparts by weight polypropylene to 1 part by weight mastering composition: 90 percent by weight polypropylene, 5 batch, e.g., in a Banbury mixer or a screw extruder propercent by Weight polyethylene, and 5 percent by weight duces a mixture containing 80 percent by weight polyethylene/propylene copolymer.

propylene and percent by weight each of ethylene/ Test pieces, /s" x /2" X 8" tensile bars were produced propylene copolymer and polyethylene. on an injection molding machine at 140 F. mold tempera- The compositions of this invention, as other thermo- 10 ture and 700 p.s.i. The test pieces were conditioned for plastic compositions, can contain stabilizers, antioxidants, a minimum of 40 hours at 23 C. and 50 percent relative colorants, processing aids, pigments, and other additives humidity prior to testing. if desired, in normal and conventional amounts. The following tests were conducted.

The polypropylene compositions of this invention can Test for: ASTM number be used to produce films, filaments, rods, protect1ve coat- Tensile yield strength D638 /mm. mgs, molded and extruded shaped art1cles, and the hke, Secant modulus D 638 O usin by procedures known in the art. These compositions form u a span g products wh1cl1 are part1cularly useful where low tempera- Melt index and melt flow tures and shock are l1kely to be encountered.

4 (melt flow 1s used for The tollowmg descr1pt1ons and examples 1llustrate the 20 1 polypropylene and poly- 1nvent1on and should not be construed as l1m1tat1ve there- To lene mixtures) D1238 44 Si and of. Unless otherwise indicated all parts and percentages P W C for p g 'p' b are by Weight ene; 44 p.s.i. and 190 EXAMPLES 1-4 C. for polyethylene,poly- A polyethylene-ethylene/propylene copolymer masterlsobutylene and ethylene/ propylene copolybatch was prepared as follows. Tnlrteen pounds of amormar l elhylane/pmpylene copolymgr l Mooney Izod impact strength D256-56 using fis' speciv1scos1ty range of from 35 to 49 and containing about mens C andos C 48 percent by weight (about 58 mole percent) combined ethylene and about 52 percent by weight (about 42 mole In Tab I data 18 presented for Examples 1-4 and percent) combined propylene and thirteen pounds of for seven COIlllOl experlments in WhlCh either (A) no polyethylene having a density of about 0.96 and a melt p y yl ne n no ethylene/propylene copolymer was index of about 5.0 were charged into a Banbury mixer. used to modify a 11.4 melt index polypropylene (Control The ethylene/propylene copolymer was added as small nly polyethylene was added to the polypropylchunks and the polyethylene as inch spherical beads. ene (Controls 25); (C) only ethylene/ propylene copoly- The two components were blended for an eight minute mer was added to the polypropylene (Controls 67). cycle at 150 C. nd then transferred to the rolls of two- It can be seen from the data collected for Examples 14, roll mill for 5 minutes, including 5 end passes before which contained both polyethylene and ethylene/propylsheeting and cutting into squares approximately 4" x 4'. ene copolymer as modifiers in accordance with this invenx These squares were fed into a Cumberland tion, that a great increase in Izod impact strength and a 7 x 10 inch plastic grinder to produce a masterbatch in decrease in tensile yield strength is attained over the conthe form of A x /8" bits. trol samples.

In Examples 1-4 an amount of masterbatch calculated Melt index is measured in declgrams per minute (dg./ to provide the desired amount of polyethylene and ethylmin.) and melt flow is measured in grams per 10 minutes ene/ propylene copolymer, as indicated in Table I follow- (g./ 10 min.).

Table I Percent by Weight Percent by Weight Percent by Weight Izod Impact Strength Example Polypropylene Polyethylene Ethylene] Tensile Yield Seeant Melt Flow. Number Melt Flo\v=1.4 Melt Index: 5 Propylene Strength Modulus g./10 mi Density=0.96 Oopolymer p.s.i. p.s.i. 23 0. 0 0

Control 1... 100 0 0' 5,000 210,000 0.40 0. 37 1 4 About 48 percent by weight combined ethylene; melt index=2.5; specific gravity=0.86; Mooney viscosity at 212 F=35 to 49.

EXAMPLE 5 The procedure of Example 1 was followed except that polyisobutylene was used. In Table II there is presented data for an experiment in which only polyethylene is used to modify the polypropylene (Control 8) and Example 5 in which both polyethylene and polyisobutylene are used as modifiers. The tensile yield strength and secant modulus of the control and the example are identical within experimental error but the Izod impact strength at 23 C. of the example has been doubled, from 3.00 to 6.00.

6 Table 11 Percent by Weight Percent by Weight Percent by Weight Izod Impact Strength Example Polypropylene, Polyethylene: Polyisobutylene, Tensile Yield Secant Melt Flow, Number Melt Floiv=1.4 Melt Idnex=5, Melt Index=0.08 Strength, p.s.i. Modulus, p.s.i. g.l min.

Denslty=0.96 23 0. 0 C.

Control 8 85 o 3,800 146, 000 3. 00 0.85 1. 42 Example 5 70 I 15 I 15 i 3,500 i 141,000 5.00 0.70 1.70

EXAMPLES 6-7 1 EXAMPLES 8-10 The procedure of Example 1 was followed except that The procedure of Example 1 was followed except that 4.0 melt flow polypropylene was use. the ethylene/propylene copolymers used were partially In Table III there is presented data for Examples 6-7 crystalline (5-20 percent) and contained 16 percent by and for seven control experiments in which either (A) no 15 weight combined propylene (Example 8); 66 percent by polyethylene and no ethylene/propylene copolymer was weight combined propylene (Example 9); or 34 percent used to modify the 4.0 melt flow polypropylene (Control by weight combined propylene (Example 10). 9); (B) only polyethylene was added to polypropylene It can be seen from the data recorded in Table V that (Controls 10-13 (C) only ethylene/ propylene copolywhen an ethylene/ propylene copolymer containing 66 permer was added to polypropylene (Controls 14-15). It cent by weight combined propylene, even though partially can be seen from the data of Examples 6-7, which concrystalline, is used (Example 9), a great increase in imtained both polyethylene and ethylene/propylene copolypact strength at 23 C. results over the control (Control mer as modifiers in accordance with this invention, that a 22) containing the same ethylene/propylene copolymer significant increase in the Izod impact strength at both and polypropylene but no polyethylene. When lower 23 C. and 0 C. and decrease in tensile yield strength is 25 amounts of combined propylene are present in the ethylattained over the control samples. ene/ propylene copolymer (Examples 8 and 10) the impact Table III Percent by Weight Percent by Weight Percent by Weight Izod Impact Strength Example Polypropylene Polyethylene Ethylene/ Tensile Yield Secant Melt Flow Number Melt Flo\v=1.4 Melt Index=5 Propylene Strength Modulus g./10 min.

Density=0.96 Copolymer a p.s.i. p.s.i. 23 0. 0 C

100 0 0 4, 900 205, 000 0. 95 5 0 5,050 185,000 0. 5s 90 10 0 4, 900 195, 000 0. 61 85 15 0 5, 000 186,000 0. 03 75 25 0 4, 950 187, 000 0. 60 90 0 10 4,000 161,000 1. 44 85 0 15 3, 500 130, 000 2. 00 so 10 i0 4, 300 155, 000 3. so 75 10 15 3, 400 127, 000 5. 10

B About 48 percent by weight combined ethylene; melt index=2.5; specific gravity=0.86; Mooney viscosity at 212 F.=35 to 49.

CONTROLS 16-20 The procedure of Example 1 was followed except that polyisoprene (Controls 16-17) and polybutadiene (Constrength is approximately the same (Example 8 at 23 C. and Example 10 at 0 C.) or higher (Example 8 at 0 C. and Example 10 at 23 C.). In Example 9 tensile yield trols 1 8-20) Were used as the rubber. Surprisingly, these strength has decreased. rubbers are not efiective in increasing the Izod impact What is claimed is: strength of the mixtures. Data for these controls are pre- 1. Polypropylene composition having high impact sented in Table IV. strength which comprises from about to about 96 per- Table IV Percent by Weight Percent by Weight Percent by Weight Percent by Weight Tensile Secant Izod Impact Strength Experiment Polypropylene Polyethylene P'olyisoprene Polybutadiene Yield Modulus,

Melt Flow=4.0 Melt Index=5 Melt Index=0. 01 Melt Index=0. 01 Strength p.s.1.

Density=0.96 p.s.1. 23 0. 0 C.

Table V Percent by Weight Percent byWeight Percent by Weight Izod Impact Strength Example Polypropylene Polyethylene Etliylene/ Tensile Yield Secant Melt Flow Number Melt Flow=1.4 Melt Index=5 Propylene. Strength, Modulus, g. [10 min.

Density=0.96 Copolymer p.s.1. p.s.1. 23 0. 0 G.

Control 21 90 0 10 4, 390 174, 000 1. 15 0. 27 1. 02 8 10 10 4, 685 184, 400 1. 17 0. 55 1. 2O 0 10 4, 315 163, 1. 67 0. 46 1. 12 80 10 10 4, 265 167, 300 2. 41 0. 45 1. 46 90 0 10 4, 350 168, 800 1. 54 0. 55 1. 06 80 10 10 4, 430 175, 300 .1. 89 0.49 1 09 Example 8: 16 percent by weight combined propylene; 84 percent by weight combined ethylene. Example 9: 66 percent by weight combined propylene; 34 percent by Weight combined ethylene. Example 10: 34 percent by weight combined propylene; 66 percent by weight combined ethylene.

cent by Weight of a normally solid polypropylene having a melt flow of less than about 12 g./ 10 min., from about 2 to about 25 percent by weight of polyethylene having a density of at least about 0.91 and a melt index of less than about 100 dg./min., and from about 2 to about 25 percent by weight of amorphous ethylene/ propylene copolymer containing from about 5 to about 75 percent by weight of combined ethylene and from about 25 to about 95 percent by weight of combined propylene and having a melt index of less than about 1000 dg./ min.

2. Polypropylene composition as claimed in claim 1 wherein the combined amount of polyethylene and amorphous ethylene/propylene copolymer is less than 35 percent by weight. I

3. Polypropylene composition as claimed in claim 1 wherein said polypropylene has a melt flow of from about 0.1 g./ 10 min. to about 2.0 g./ 10 min., aid polyethylene has a melt index of from about 1.0 dg./min. to about 8 dg./ min. and said amorphous ethylene/propylene copolymer has a melt index of less than about 100 dg./min. I

4. Polypropylene composition as claimed in claim 3 wherein the combined amount of polyethylene and ethylene/ propylene copolymer in said polypropylene composition is less than percent by weight.

5. Polypropylene composition having high impact strength which comprises from about to about 92 percent by Weight of a normally solid polypropylene having a melt flow of from about 0.1 g./ 10 min. to about 2.0 g./ 10 min., from about 4 to about 20 percent by Weight of polyethylene having a density of about 0.96 and a melt index of from about 1.0 dg./min. to about 8.0 dg./min. and from about 4 to about 15 percent by weight of ethylene/propylene copolymer having a melt index of less than about 100 dg./min. and containing from about 35 to about percent by weight of combined ethylene and from about 20 to about 65 percent by weight of combined propylene.

References'Cited by the Examiner UNITED STATES PATENTS 2,993,028 7/1961 Ranalli 260-897 3,036,987 5/1962 Ranalli 260897 MURRAY TILLMAN, Primary Examiner.

LEON I. BERCOVITZ, Examiner. 

1. POLYPROPYLENE COMPOSITION HAVING HIGH IMPACT STRENGTH WHICH COMPRISES FROM ABOUT 50 TO ABOUT 96 PERCENT BY WEIGHT OF A NORMALLY SOLID POLYPROPYLENE HAVING A MELT FLOW OF LESS THAN ABOUT 12 G./10 MIN., FROM ABOUT 2 TO ABOUT 25 PERCENT BY WEIGHT OF POLYETHYLENE HAVING A DENSITY OF AT LEAST ABOUT 0.91 AND A MELT INDEX OF LESS THAN ABOUT 100 DG./MIN., AND FROM ABOUT 2 TO ABOUT 25 PERCENT BY WEIGHT OF AMORPHOUS ETHYLENE/PROPYLENE COPOLYMER CONTAINING FROM ABOUT 5 TO ABOUT 75 PERCENT BY WEIGHT OF COMBINED ETHYLENE AND FROM ABOUT 25 TO ABOUT 95 PERCENT BY WEIGHT OF COMBINED PROPYLENE AND HAVING A MELT INDEX OF LESS THAN ABOUT 1000 DG./MIN. 